Method of epoxidizing olefins

ABSTRACT

A process is provided for the epoxidation of olefins with percarboxylic acid in a reaction mixture consisting of an aqueous phase and an organic phase, the percarboxylic acid being formed in situ in the aqueous phase from hydrogen peroxide and a carboxylic acid or a carboxylic anhydride, and the olefins being dissolved in an organic solvent in the organic phase, wherein the epoxidation is carried out in several steps, each step being carried out with a fresh aqueous phase and the aqueous phase being separated off after each step.

This application is a 371 of PCT/EP99/08079 filed Oct. 26, 1999.

The invention relates to a process for the epoxidation of olefins in atwo-phase reaction system with percarboxylic acids formed in situ.

Epoxides of olefinically unsaturated compounds represent an importantclass of intermediates. In a process known for a long time, olefins areepoxidized by reaction with percarboxylic acids, which can be producedin situ from hydrogen peroxide and carboxylic acids. By scission, theoxiran ring formed in place of the olefinic double bond can react with alarge number of compounds containing active hydrogen, thereby opening upan extensive secondary chemistry.

In the processes of the state of the art, the reactivity of epoxidesresults in the formation of by-products. Thus epoxides react in thepresence of water and carboxylic acids to give glycols or their mono-and diester, the scission of the oxiran ring being acid-catalyzed. Theproblem here is that the formation of the percarboxylic acid is alsoacid-catalyzed, so the process is often carried out in the presence ofmineral acids as catalysts.

DE-B 1 230 005 discloses a process for the epoxidation of linearalpha-olefins which uses peracetic acid free of water and mineral acidas the epoxidizing reagent and is carried out in the presence of aninert solvent such as acetone, methyl acetate or ethyl acetate. Thedisadvantages are the long reaction times of several hours, theincomplete olefin conversion and the high proportion of by-products,especially glycol monoester. Also, the epoxidizing reagent used isexpensive.

DE-C 195 19 887 describes a process for the epoxidation of olefinicallyunsaturated compounds with percarboxylic acid prepared in situ, saidprocess being carried out with water as the only solvent and in thepresence of inhibitors. No information is given on the exact compositionof the product mixture.

DE-A 15 68 016 discloses a process in which alpha-olefins are epoxidizedin a water-immiscible solvent with a percarboxylic acid formed in situin the aqueous phase, the reaction mixture being stirred in such a wayas to maintain a single phase interface. This procedure demands verylong reaction times.

EP-A 0 032 989 describes a process for the epoxidation of alpha-olefinswith performic acid formed in situ, said process being carried out inthe absence of a solvent and an acid catalyst. Epoxidation by thisprocess demands a long overall reaction time. Also, the olefinconversion is unsatisfactory despite the long reaction time.

It is an object of the present invention to provide a process for theepoxidation of olefins in which a quantitative conversion is achievedand products of high purity are obtained after short reaction times.

We have found that this object is achieved by a process for theepoxidation of olefins with percarboxylic acid in a reaction mixtureconsisting of an aqueous phase and an organic phase, the percarboxylicacid being formed in situ in the aqueous phase from hydrogen peroxideand a carboxylic acid or a carboxylic anhydride, and the olefins beingdissolved in an organic solvent in the organic phase. The processaccording to the invention comprises carrying out the epoxidation inseveral steps, each step being carried out with a fresh aqueous phaseand the aqueous phase being separated off after each step.

In terms of the present invention, olefins are compounds containing oneor more olefinic double bonds. Examples of compounds with olefinicdouble bonds are linear or branched mono- and diolefins having from 6 to30 C atoms, unsaturated, optionally hydroxy-substituted fatty acidshaving from 6 to 24 C atoms and from 1 to 5 double bonds, their estersor triglycerides, and unsaturated alcohols having from 6 to 24 C atomsand from 1 to 3 double bonds. Polyalkenes and terpenes are also olefinsin terms of the present invention. In addition to the double bond(s),the olefins can contain other functional groups which do not react, orreact only slowly, with the solvent or the epoxidizing reagent under thereaction conditions. For example, the olefins can contain heteroatoms,such as an ether oxygen, or can be substituted by hydroxyl groups,carboxylic acid groups, carboxamide, carboximide, carboxylic acid ester,lactam or lactone groups, aromatic radicals or halogen atoms. The olefinused may already contain epoxy groups, keto groups or cyclic carbonategroups.

Examples of suitable olefins are mono- or diolefins having from 6 to 30C atoms, preferably from 10 to 24 C atoms and particularly preferablyfrom 12 to 18 C atoms, which can be branched or unbranched. Branchedolefins can also be branched on the double bonds. Both cis and transisomers can be used. Examples are 1-hexene, 2-hexene, 3-hexene,1,3-hexadiene, 1,4-hexadiene, 3-methyl-1,3-pentadiene,2-methyl-1-pentene, 3,3-dimethyl-1-butene, 1-heptene, 3-heptene,1-octene, 4-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene,1-tetradecene, 1-hexadecene, 1-octadecene. The preferred olefins arelinear, for example the linear olefins mentioned above, of which thosewith a terminal double bond (linear alpha-olefins) are particularlypreferred. Of the linear alpha-olefins, those with an even number of Catoms are particularly preferred because of their ready availabilityfrom petrochemical processes.

Other suitable olefins are cyclic olefins such as cyclohexene,cyclooctene, cyclooctadiene, cyclodecene and cyclododecene, and theirsubstituted derivatives, for example substituted cyclohexenes such as1,3-dimethylcyclohexene, 1,4-dimethylcyclohexene or 1-ethylcyclohexene.

Other suitable olefins are terpenes, terpene alcohols and other naturalsubstances with one or more double bonds, such as steroids. In additionto the olefinic double bonds, these can contain other functional groupssuch as hydroxyl or keto groups. Examples are 2-carene, delta-3-carene,alpha-pinene, beta-pinene, verbenol, myrtenol, cis-jasmone,dihydrocarveol, alpha-terpinene, gamma-terpinene, alpha-ionone,beta-ionone, limonene, carvone, citronellic acid, trans-vaccenic acid,geraniol, farnesol, phytol, citronellol, ergosterol, myrcene, squaleneand camphene.

Other suitable olefins are unsaturated fatty acids having from 6 to 24 Catoms and from 1 to 5 double bonds, which can optionally be substitutedby hydroxyl groups, for example oleic acid, elaidic acid, linoleic acid,linolenic acid, arachidonic acid, linolenelaidic acid, linoelaidic acid,myristoleic acid, palmitoleic acid, undecenoic acid or ricinoleic acid.Other suitable olefins are the esters of unsaturated fatty acids,especially their triglycerides such as those which occur in animal andvegetable fats and oils, for example in soya oil, sunflower oil, linseedoil, rapeseed oil, colza oil, groundnut oil, palm oil, coconut oil,castor oil, tallow, lard and fish oil. Other suitable olefins areunsaturated fatty alcohols having from 1 to 3 double bonds, such asoleyl alcohol, elaidyl alcohol, linoleyl alcohol, linolenyl alcohol andarachidonyl alcohol.

Other preferred olefins are polyalkylenes such as polyisobutene.

The olefins are dissolved in an organic solvent. Suitable organicsolvents form a two-phase reaction system with the epoxidizing reagentconsisting of a carboxylic acid and aqueous hydrogen peroxide solution,so they are water-immiscible organic solvents or organic solvents havingonly a limited miscibility with water. The organic solvents are used inan amount appropriate for the formation of an organic phase separatedfrom the aqueous phase. Solvents which are completely miscible withwater are therefore unsuitable.

Preferred organic solvents are also inert toward aqueous hydrogenperoxide solution, carboxylic acids and percarboxylic acids andespecially toward the epoxides formed. Preferred solvents have amarkedly different density from that of water, hydrogen peroxidesolution or the aqueous carboxylic acid solution.

Preferred organic solvents have at least a limited miscibility withwater. The water absorption capacity of the organic solvent at 25° C. ispreferably at least 0.1 and at most 10 mol %, particularly preferably atleast 0.1 and at most 5 mol %, very particularly preferably at least 0.2and at most 2 mol % and especially at least 0.2 and at most 1.0 mol %.

Examples of suitable solvents are aliphatic and aromatic hydrocarbonsand halogenohydrocarbons such as pentanes, hexanes, heptanes, octanes,cyclopentane, cyclohexane, methylcyclopentane, methylcyclohexane,dichloromethane, chloroform, carbon tetrachloride, trichloroethane,benzene, toluene, xylenes, ethylbenzene, chlorobenzene anddichlorobenzenes, and also aliphatic and alicyclic ethers such asdiethyl ether, dipropyl ether, diisopropyl ether, tetrahydrofuran anddioxane. Aromatic hydrocarbons such as benzene, chlorobenzene, toluene,ortho-, meta- and para-xylene and ethylbenzene, and halogenohydrocarbonssuch as dichloromethane, chloroform and chlorobenzene, are particularlypreferred because their water absorption capacity is sufficiently highbut limited and their reactivity is low. The weight ratio of olefin tosolvent generally ranges from 1:100 to 10:1, preferably from 1:10 to 2:1and particularly preferably from 1:5 to 1:1.

The percarboxylic acid is formed in situ in the aqueous phase from acarboxylic acid or a carboxylic anhydride and aqueous hydrogen peroxidesolution.

Suitable carboxylic acids are those which are at least partially solublein the aqueous phase at the reaction temperature, such as at leastpartially water-miscible aliphatic, araliphatic and aromatic carboxylicacids. Examples are formic acid, acetic acid, chloroacetic acid,dichloroacetic acid, trichloroacetic acid, phenylacetic acid,trifluoroacetic acid, propionic acid, benzoic acid, meta-chlorobenzoicacid and phthalic acid. It is also possible to use carboxylicanhydrides, for example maleic anhydride. Preferred carboxylic acidshave a high solubility in water and a low solubility in the organicsolvents used. Particularly preferred carboxylic acids are miscible withwater in all proportions. Examples of preferred carboxylic acids arealiphatic carboxylic acids having from 1 to 3 C atoms, such as formicacid, acetic acid and propionic acid. Maleic anhydride is alsopreferred. Acetic acid and formic acid are particularly preferred andformic acid is very particularly preferred.

The hydrogen peroxide solution used is generally an aqueous hydrogenperoxide solution with a concentration of 3 to 95% by weight, preferablyof 10 to 90% by weight, particularly preferably of 30 to 85% by weightand especially of 50 to 80% by weight.

The epoxidation is carried out in several steps, a fresh aqueous phasebeing used in each step. In each individual step, it is possible tointroduce the full amount of carboxylic acid all at once or to introduceonly part of the carboxylic acid and, where appropriate, to add theremainder of the carboxylic acid and the hydrogen peroxide solution inportions or continuously. The first variant is the preferred procedure,it being particularly preferred to introduce the full amount ofcarboxylic acid and to run the hydrogen peroxide solution incontinuously. The aqueous phase is dispersed as droplets in the organicphase in each step, preferably by stirring.

The molar ratio of the amounts of hydrogen peroxide and carboxylic acidused per step (based on monocarboxylic acids) generally ranges from100:1 to 1:10, preferably from 10:1 to 1:2, particularly preferably from5:1 to 1:2 and very particularly preferably from 2:1 to 1:2. This ratiocan differ from step to step.

The molar ratio of the total amount of hydrogen peroxide used in all thesteps to the amount of olefin used is generally at least stoichiometric,i.e. (based on monoolefins) at least 1:1, preferably 5:1 to 1:1 andparticularly preferably 2:1 to 1:1.

The epoxidation is carried out preferably in two to four steps andparticularly preferably in three or four steps. The amount of hydrogenperoxide used per step can be the same or different. Preferably, theamount of hydrogen peroxide used per step will decrease with increasingolefin conversion. The amount of carboxylic acid used per step can alsobe the same or different. Preferably, the amount of carboxylic acid usedper step will decrease from step to step with increasing olefinconversion, especially when the amount of hydrogen peroxide used perstep also decreases from step to step.

In one preferred embodiment of the process according to the invention,the amount of hydrogen peroxide used in the first step will bestoichiometric, based on olefin, i.e. one mol of hydrogen peroxide permol of olefinic double bonds, and in every other step will be smallerbut in total not more than two mol and particularly preferably not morethan 1.5 mol.

In another preferred embodiment, the amount of hydrogen peroxide used inthe first step will be substoichiometric, based on olefin, preferably0.5 mol of hydrogen peroxide per mol of olefinic double bond, and inevery other step will be smaller but in total not more than 1.5 mol andparticularly preferably not more than 1.2 mol.

In another preferred embodiment, the epoxidation is carried out in sucha way that generally 30 to 90% and preferably 30 to 70% of the olefinhas been converted after the first step. If the process according to theinvention is carried out in at least three steps, the olefin conversionis generally 50 to 95% and preferably 60 to 90% after the second step.The progress of the reaction can be monitored by gas chromatography ortitrimetry, for example by determining the iodine number or the epoxycontent, and an epoxidation step can be interrupted by phase separationwhen a particular conversion is reached.

After each step, the aqueous phase is separated off and replaced with afresh aqueous phase. It is not absolutely necessary here for thepercarboxylic acid and/or hydrogen peroxide to have reacted completely,although this is desirable if the peracid is to be utilized efficiently.

The epoxidation reaction is preferably carried out under atmosphericpressure. The reaction temperature depends on the chain length of theolefin and is generally 60 to 100° C. The reaction can be carried out inconventional reaction apparatuses, such as a stirred tank or stirredtank cascade, with conventional phase separation devices. The reactionis preferably carried out under reflux, the condenser used ensuringadequate heat dissipation.

The process according to the invention has a number of advantages. Thusthe total duration of the epoxidation reaction is short, being generally<10 h, preferably <7 h and particularly preferably <5 h for an olefinconversion of at least 95% by weight, preferably of at least 98% byweight. The reaction time is preferably <1 h per step.

An epoxide of high purity is formed in the process according to theinvention. The epoxy content of the crude product is generally >90 mol%, preferably >95 mol %, based on the olefin used. The glycol content isgenerally <5% by weight, preferably <2% by weight, and the total contentof other secondary constituents, such as the glycol monoesters anddiesters of the carboxylic acids used, is generally <5 mol %, preferably<2 mol %.

Changing the aqueous phase maintains a sufficiently high carboxylic acidconcentration and hydrogen peroxide concentration in the aqueous phaseto avoid the use of mineral acids as catalysts for formation of theperoxide.

On the one hand, carrying out the process in a two-phase reaction systemsubstantially suppresses secondary reactions of the epoxides present inthe organic phase with water or the carboxylic acid present in theaqueous phase, for example the acid-catalyzed scission of the oxiranring to form glycols, monoesters and diesters. The risk of formingby-products can be further lowered by reducing the amount of carboxylicacid in the aqueous phase as the olefin conversion progresses.

On the other hand, choosing a suitable solvent of sufficiently highpolarity (water absorption capacity) ensures effective transport of thepercarboxylic acid into the organic phase and hence a sufficiently highreaction rate.

The product obtained can be used without further purification, ifappropriate after distillation of the solvent. When using e.g. tolueneas the organic solvent and formic acid as the carboxylic acid, anytraces of formic acid and water are entrained out as an azeotrope togive a substantially dry and acid-free product. The same applies to thesystems toluene/ acetic acid/water, xylene/acetic acid/water, xylene/formic acid/water and dichloromethane/formic acid/ water. If very highdemands are made on product purity, it is possible to carry out a finedistillation under reduced pressure.

The invention is illustrated in greater detail by means of the exampleswhich follow.

EXAMPLES Example 1

336 g of 1-dodecene (2.0 mol), 800 g of toluene and 46 g of concentratedformic acid (99% by weight, 1.0 mol) are placed in a 2 l flask andheated to 90° C. In a first step, 136 g of hydrogen peroxide solution(50% by weight, 2.0 mol) are added dropwise over a period of 20 min tothe intensely stirred mixture and stirring is then continued for afurther 20 min. The aqueous phase is separated off. In the second tofourth steps, the indicated amounts of formic acid are added all at onceand the indicated amounts of hydrogen peroxide (concentrations andtemperature as above) are added dropwise over a period of 5 min in eachstep, stirring is continued for 20 min in each step and the aqueousphase is then separated off.

2nd step: 0.5 mol of formic acid and 0.5 mol of hydrogen peroxide; 3rdand 4th steps: in each case 0.3 mol of formic acid and 0.3 mol ofhydrogen peroxide.

This gives a crude product of the following composition (in GC area %):1,2-epoxydodecane 93.2%, 1-dodecene 1.1%, 1,2-dodecanediol 2.1%,1,2-dodecanediol monoformyl ester and 1,2-dodecanediol diformyl ester1.6%.

Example 2

168 g of 1-dodecene (1.0 mol), 400 g of dichloromethane and 96 g ofconcentrated formic acid (99% by weight, 1.5 mol) are placed in a 1 lflask and heated to 90° C. In a first step, 102 g of hydrogen peroxidesolution (50% by weight, 1.5 mol) are added dropwise over a period of 5min to the intensely stirred mixture and stirring is then continued fora further 45 min. The aqueous phase is separated off. In the second andthird steps, the indicated amounts of formic acid are added all at onceand the indicated amounts of hydrogen peroxide (concentrations andtemperature as above) are added dropwise over a period of 5 min in eachstep, stirring is continued for 45 min in each step and the aqueousphase is then separated off.

2nd step: 0.5 mol of formic acid and 0.5 mol of hydrogen peroxide; 3rdstep: 0.3 mol of formic acid and 0.3 mol of hydrogen peroxide. Thisgives a crude product containing 94.5% by weight of 1,2-epoxydodecane.

Example 3

2295.3 g of polyisobutene 1000 (3.0 mol), 1200 g of toluene and 92 g ofconcentrated formic acid (99% by weight, 2.0 mol) are placed in a 5 lflask and heated to 90° C. In a first step, 136 g of hydrogen peroxidesolution (50% by weight, 2.0 mol) are added dropwise over a period of 40min to the intensely stirred mixture and stirring is then continued fora further 45 min. The aqueous phase is separated off. In the secondstep, 0.5 mol of formic acid is added all at once, 0.5 mol of hydrogenperoxide (concentrations and temperature as above) is added dropwiseover a period of 20 min, stirring is continued for 60 min and theaqueous phase is then separated off to give the epoxide in quantitativeyield.

Example 4

2295.3 g of polyisobutene 1000 (3.0 mol), 1200 g of toluene and 92 g ofconcentrated formic acid (99% by weight, 2.0 mol) are placed in a 5 lreactor and heated to 90° C. In a first step, 136 g of hydrogen peroxidesolution (50% by weight, 2.0 mol) are added dropwise over a period of 40min to the intensely stirred mixture and stirring is then continued fora further 60 min. The aqueous phase is separated off. In the secondstep, 46 g (1.0 mol) of formic acid are added all at once, 68 g (1.0mol) of hydrogen peroxide (concentrations and temperature as above) areadded dropwise over a period of 20 min, stirring is continued for 60min, the aqueous phase is then separated off and the organic phase isconcentrated under reduced pressure to give the epoxide in quantitativeyield.

Example 5

2295.3 g of polyisobutene 1000 (3.0 mol), 983.7 g of Mihagol®M (amixture of C₁₀-C₁₄ n-paraffins) and 92 g of concentrated formic acid(99% by weight, 2.0 mol) are placed in a 10 l reactor and heated to 90°C. In a first step, 136 g of hydrogen peroxide solution (50% by weight,2.0 mol) are added dropwise over a period of 20 min to the intenselystirred mixture and stirring is then continued for a further 60 min. Theaqueous phase is separated off. In the second step, 46 g (1.0 mol) offormic acid are added all at once, 1.0 mol of hydrogen peroxide(concentrations and temperature as above) is added dropwise over aperiod of 10 min, stirring is continued for 60 min and the aqueous phaseis then separated off. 300 ml of toluene are then added to the organicphase, and water and formic acid are removed by distillation. Finally,the organic phase is concentrated under reduced pressure to give theepoxide in quantitative yield.

Comparative Example C1

168 g of 1-dodecene (1.0 mol) are mixed with 92 g of concentrated formicacid (99% by weight, 2.0 mol). 81.6 g of hydrogen peroxide (50% byweight, 1.2 mol) are added dropwise at 90° C. over a period of 15 min tothe intensely stirred mixture and intense stirring is then continued at90° C. for a further 2 h. The course of the reaction is monitored bytitration of the amount of peracid/peroxide. When the reaction hasended, the phases are separated at 80° C. and the organic phase isanalyzed by gas chromatography.

209 g of a low-melting colorless solid of the following composition (inGC area %) are obtained: 1,2-dodecanediol 73.4%, 1,2-dodecanediol1-monoformyl ester 9.8%, 1,2-dodecanediol 2-monoformyl ester 15.9%,1,2-dodecanediol diformyl ester 0.9%.

We claim:
 1. A process for the epoxidation of olefins with percarboxylicacid in a reaction mixture consisting of an aqueous phase and an organicphase, the percarboxylic acid being formed in situ in the aqueous phasefrom hydrogen peroxide and a carboxylic acid or a carboxylic anhydride,and the olefins being dissolved in an organic solvent in the organicphase, which process comprises carrying out the epoxidation in severalsteps, each step being carried out with a fresh aqueous phase and theaqueous phase being separated off after each step.
 2. A process asclaimed in claim 1, wherein the water absorption capacity of the organicsolvent at 25° C. is at least 0.1 and at most 10 mol %.
 3. A process asclaimed in claim 1, wherein the organic solvent is selected frombenzene, toluene, ortho-, meta- and para-xylene, ethylbenzene andhalogenhydrocarbons.
 4. A process as claimed in claim 1, wherein thecarboxylic acid or carboxylic anhydride is selected from formic acid,acetic acid, propionic acid and maleic anhydride.
 5. A process asclaimed in claim 1, wherein the carboxylic acid is formic acid.
 6. Aprocess as claimed in claim 1, wherein linear alpha-olefins having from6 to 30 C atoms are epoxidized.
 7. A process as claimed in claim 1,wherein the amount of hydrogen peroxide used per step decreases fromstep to step.
 8. A process as claimed in claim 1, wherein the amount ofacid used per step decreases from step to step.
 9. A process as claimedin claim 1, wherein the epoxidation is carried out in at least threesteps in such a way that the olefin conversion is 30 to 70% after thefirst step and 50 to 90% after the second step.
 10. A process as claimedin claim 1, wherein the epoxidation is carried out under atmosphericpressure and at a temperature of 60 to 100° C.
 11. A process as claimedin claim 1, wherein polyisobutene is epoxidized.